This invention relates to the art of hydraulic power units and, more particularly, to the piston-cylinder portion of such hydraulic units.
Particular utility of this invention is found in a power unit for controlling operation of a plow blade mounted on a vehicle, and the invention will be described herein with reference thereto. However, it will be appreciated that the invention has broader applications and may be used for controlling other devices.
Plow blades are often mounted on the front of a vehicle for the purpose of being pushed by the vehicle to clear snow, ice or other debris when the plow blade is lowered to a roadway. The plow blade is pivotally connected to a mounting frame secured to a frame portion of the vehicle and is also connected to a movable lift arm by a link chain. The lift arm is also supported by the mounting frame and is movable vertically, relative to the vehicle, to cause up and down movement of the plow blade relative to the roadway. A power unit is positioned between the mounting frame and the lift arm. The power unit generally includes a piston-cylinder unit which is functionally connected between the lift arm and mounting frame to cause the lift arm to raise when the piston is extended from within the cylinder, and to lower when the piston retracts into the cylinder. Usually, such retraction is caused by the weight of the plow blade after relieving the hydraulic pressure in the cylinder. In addition to the blade lifting and lowering piston-cylinder unit, the power unit for positioning the plow blade includes a motor-pump unit, and a number of control valves for additional hydraulic piston-cylinder units operable to achieve other blade displacement functions.
In this respect, the plow blade is usually power controlled for sideways angling as well as up and down movement. The additional piston-cylinder units mentioned above are provided on the plow blade unit for this purpose. U.S. Pat. No. 3,706,144 describes a device of the type discussed above and discloses an integral power unit assembly mounted at the front of a vehicle. The integral power unit advantageously incorporates the lift piston-cylinder, the motor-pump and the control valves in a unitary assembly. An integral power unit of this character is advantageous from the standpoint of compactness, and manufacturing and mounting ease and economy. One structural example of such a power unit is shown in U.S. Pat. No. 3,773,074. The disclosures of the above two patents are incorporated herein by reference.
While such an integral power unit lends itself to mounting on the front of a vehicle, by such mounting it is exposed to weather and other undesirable exterior factors. Some purchasers of plow blade arrangements prefer that the power unit components including the motor-pump and valves not be so exposed and, thus, specify that the hydraulic controls and motor-pump unit be internal to the vehicle, such as within the engine compartment. The location of a plow blade relative to a vehicle and the number of plow blades provided on the vehicle also has bearing upon location of the power unit components relative to the vehicle. In this respect, such an integral power unit heretofore had to be mounted on the vehicle front because of the structural relationship between the lift piston-cylinder and motor-pump units. Thus, use of the integral power unit was limited to front end mounting applications and, accordingly, all of the advantages of manufacturing and mounting economy and compactness were likewise limited. Prior to the present invention, specifications of a purchaser requiring a remote location for the controls of a plow blade power unit could not be met with an integral power unit of the character described above and required manufacturing an entirely different unit.